Spin excitations in cubic maghemite nanoparticles studied by time-of-flight neutron spectroscopy

Wetterskog, E.; Salazar-Alvarez, G.; Podlesnyak, A. A.; Hermann, Raphael; Hyeon, T.; An, K.; Bergström, L.; Brückel, Th.; Disch, Sabrina

doi:10.1103/PhysRevB.89.064402

Journal Article

FZJ-2014-01382

Spin excitations in cubic maghemite nanoparticles studied by time-of-flight neutron spectroscopy

Wetterskog, E. ; Disch, S. (Corresponding author) ; Podlesnyak, A. A. ; An, K. ; Hyeon, T. ; Salazar-Alvarez, G. ; Bergström, L.FZJ* ; Brückel, T.FZJ* ; Hermann, R.FZJ*

2014
APS College Park, Md.

Physical review / B 89(6), 064402 (2014) [10.1103/PhysRevB.89.064402]

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Please use a persistent id in citations: http://hdl.handle.net/2128/5939 doi:10.1103/PhysRevB.89.064402

Abstract: We have determined the field dependence of collective magnetic excitations in iron oxide nanoparticles of cubic shape with 8.42(2) nm edge length and a narrow log normal size distribution of 8.2(2)% using time-of-flight neutron spectroscopy. The energy dependence of the uniform precession modes was investigated up to 5 T applied field and yields a Landé factor g=2.05(2) as expected for maghemite (γ-Fe2O3) nanoparticles. A large effective anisotropy field of BA,eff=0.45(16) T was determined, in excellent agreement with macroscopic measurements. This anisotropy is attributed to enhanced shape anisotropy in these monodisperse cubic nanoparticles. The combination of our results with macroscopic magnetization information provides a consistent view of the energy scales of superparamagnetic relaxation and collective magnetic excitations in magnetic nanoparticles.

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